Process of making reflecting electric lamps



Aug. 24, 1943.

c. BIRDSEYE ETA-L .PROCESS OF MAKING REFLECTING ELECTRIQ LAMPS Original Filed Nov.-25, 1938 www. @at

T l /f//l l, ...HIV

114 vnfoz Clarence Birdseye, Gloucester. Mass., and Pincus Deren, Milwaukee, Wis., assimrs to Birdseye Electric Corporation, Gloucester, Mass., a corporation of Massachusetts f original application November z's, 193s, sei-ln No. 242,216. Divided vand this application Maren 14, 1940, semi N0. 323,928 f 4 claims. ,(cl. 117-35)4 'Ihe present invention relates to electric lamps and consists in an improved redecting lamp having certain advantages over those heretofore available. The invention includes within its scope the process herein disclosed of producingsuch improved reecting lamps. In reflecting electric lamps in which the light source is hooded by a. reflecting surface formed upon the bulb there is a tendency for the reflected rays to project a shadowof the mount and filament supports or an image of the incandescent filament and to produce thereby a light pattern that is irregular in intensity and unpleasant to the eye.

Heretofore this objectionable tendency has been eliminated to some extent by frosting the transmitting area of the bulb either on the inside or the outside. The frosted transmitting area diffuses the light emitted by the bulb so as to eliminate or largely reduce uneven light intensity patterns cast on the illuminated area.

There is however, a serious objection incident to the practice above discussed. When practically all the light rays from the incandescent filament are directed by the reflecting surface through the transmitting area of the bulb the concentration of light is so great that the glass of the bulb in this area, when frosted in the usual commercial manner, becomes intensely brilliant. This frosted transmitting area even becomes so bright that, particularly in lamps of high Wattage, it is unpleasant to observe directly despite the fact that the filament may be completely hooded by the opaque reflecting portion of the bulb. In fact, a lamp frosted for direct illumination 'in the customary manner when viewed from the' side is very much brighter throughout its transmittingarea than a similar lamp without any frosting.

In oui` prior Patent No. 2,144,673, granted January 2li, 1939, of which the present application is a continuation as to lall common subject matter, we have disclosed a method of preventing In one aspect the present invention consists in a reflecting electric lamp in which substantially the entire inner. surface of the bulb is processed so that it` presents a continuous contour of smooth rounded depressions, the reecting coating being applied' to this surface in the desired 1 areas as metal deposited orevaporated directly the formation of shadows and bright'ima'ges in A the illuminated areas by applying a diffusing reflector to the surface of the bulb. In one aspect the present invention consists lin animprovement over that disclosed in oui` said .prior applicatiom'viz., we lcontrol thediffusion of the reflected light by avcombination fof two expedients each however, modified to an-extent that would make-either of, them yalone inadequateffor' the purpose, and which at the same time, avoids certain very real diillculties inherent to each of said expedients if unmodified.

upon the processed surface of the bulb and thereby given a diffusing reflecting characteristic. The configuration imparted to the bulb by the suggested treatment is hardly adequate to give to the metal deposited upon it a pronounced diffusing character suilicient to eliminate shadows,

nor will the same treatment of the transmitting l area accomplish this en d by itself. However, by combining the diffusing reflecting surface thus produced and the diffusing transmitting surface in cooperative relation, so that theirindividual effects are additive, the final result is highly satisfactory in eliminating shadows in the illuminated area. Moreover, this is accomplished without causing the transmitting area to glow with a high degree of brilliancy. Further, the

processed transmitting areav diverts but a slight amount of light as compared tothe amount which is lost in a corresponding area which has been frosted by the commercial processes heretofore practiced and there is practically no loss of llight within the lamp at any point of diffusing reflection since the metallic coating preferably may be applied to the inner surface of the bulb so inner surface of the bulb in themanner lde-` scribed, then applying a metallic `reflecting coat'- ing to the internal processed surface vand finally,` removing the vmetal coating by means of la.

chemical solution to define a transmitting area in the lamp. Heretofore it has beenthe general practice' when applying a reflecting coating of silveroralinriinuxn to theintern'al surfacey of' lamp bulbs to coat substantially lthementirebulb surface and tthenfto remove the. metal, coating by mechanical means from ithose 'areas that are'v to transmit-light. IItis extremely difflcultgtofre-" o moveafmetallic coatingf'by mechanical; means f' froml a glass' surfaceprocessed 'and sdminutely' roughened in the manner of our invention. We

- accordingly contemplate the removal of the metal coating by chemical solution, for example, by

tion andan illustrative example of a reectin8` electric lamp embodying our invention. In the drawing- Fig. 1 is a view in elevation, with parts broken away, suggesting the step of depositing a metallic reflecting coating upon the inner surface of a processed bulb, and includes a section of the bulb wall as seen magnied approximately 500 removing the metallic coating from the transtimes in the field of a microscope,

Fig. 2 is a similar view suggesting the step of mitting area of the coated bulb," and Fig. 3 is a view in elevation ofthe complete lamp, and also includes a section of the bulb wall as seen in the eld of a microscope.

The first step in the processof our invention is to provide substantially the entire inner surface of the bulb with a particular conguration of contour which, for want of a better term, we will call a shell surface. By this we mean a contour of shallow rounded depressions or hollows which covers substantially the whole surface, and hasno deep valleys, no sharp peaks and no flat facet faces, but merely gently scooped and rounded depressions. 'Ihe individual depressions or hollows are of varied size, irregular in shape and appear to be bounded by straight or slightly curved lines extending in all directions and meeting in vertices sometimes in pairs and sometimes in greater numbers. In Fig. 1 the characteristic surface is represented as actually observed in the ileld of a microscope at a magnification of 300 to 500. Heretofore frosting imparted to bulbs has been characterized by deep cavities with steep sides which under the microscope look in some places like the facets of crystals and in other places present sharply concave surfaces. These actually act to reflect the light back and forth from side to side of the pits or cavities and create much greater disturbances and absorption of the light than does the type of configuration employed in accordance with our invention. Our novel configuration of surface, on the contrary, does not substantially interfere with the directional characteristics of the lamp, that is to say, the reflecting surfaces of the lamp define the beam in which the light is emitted and the reflecting or diifusing effect of the shell surface is not such as to deflect any substantial amount of light outside this beam. The effect We'desire is a slight differential refraction of the light passing through the transmitting section of the hub in a heterogeneous manner, that is, the emergence angle of each ray is only slightly different from the straight line it would follow in emerging from an unprocessed bulb.

The present commercial process of frosting bulbs isfully disclosed in U. S. Letters Patent No. 1,687,510, October 16, 1928, Pipkin. The process of that patent involves the use of two different frosting solutions of the same composition, the second used being merely weaker than4 the first. In providing the shell surface characteristic or our invention, we may take a bulb frosted or etched in accordance with the complete process of the Pipkin patent and strip the frosting by using a stripping solution, for example, a 25% hydrofluoric acid solution having added thereto 5%v ammonium bluoride and preferably used hot.Y The proportions given are not critical,v but are merely illustrative of one satisfactory stripping solution. The eect of this solution in the bulb is to smooth out the frosted surface of the glass into approximately shallow curved recesses of the general shape shown in Fig. l -of the drawing. Alternatively the desired shell surface may be produced by first treating the interior of the bulb with any commercial frosting solution and then processing it in the manner already explained.

It will be understood that the stripping solution used in -the process of our invention is not a. frostingor an etching solution and is not effective for such purposes. Moreover the shell surface we produced is characteristically different from any frosted surface known before oui discovery. and as such constitutes an important aspectof our invention.

Having first provided the desired shell surface in the bulb, 'the next step of the process is to apply a metallic reflecting coating thereto. One process of applying such metallic coating is disclosed in U. S. Letters Patent No. 2,237,328, dated April 8, 1941, and granted on our copending application, Ser. No, 101,943, filed February 19, 1938, In Fig. 1 is illustrated the step of vaporizing silver or aluminum to form a. reflecting coating in the manner more fully disclosed in our said application. The processed bulb I0 is inverted over a pair of electrodes Il and I2, sealed and exhausted. Between the electrodes is mounted a. boat or receptacle I3 in which is placed a charge of metal for the coating. The exhausted bulb is heated and the metal charge reduced to a molten state which the bulb is maintained under vacuum so that any gases evolved from thev metal charge are immediately removed from the bulb. The charge in the boat I3 is then quickly raised to the vaporizing point of the metal by electrical energy transmitted 'to the electrodes II and I2. 'I'he metal is thus flashed and deposited upon the shell surface of the inner walls of the exhausted bulb.

In this operation a diffusing reflecting surface is formed of the general character disclosed in our prior Patent No. 2,144,663 already identified. 'I'he structure of this reflecting surface is indicated in Fig. 3 of Vthe drawing from which it will be seen that the gently sloping rounded hollows and depressions of the shell surface are now coated with a' thin deposit of metal I9 thereby' forming a reflector which is mildly diffusing, that is to say, in which the reflected rays are slightly but not violently deflected from the normal paths which they would follow if specularly reflected from' the surface of unprocessed walls. Our object is to provide a reflecting surface having a relatively slight diffusing action which is combined in its effect with the relativelyy slight diffusing action of the shell surfaced transmitting portion of the lamp. The cooperative effect of these two factors produces the desired results in eliminating shadows and bright images in the area illuminated by the lamp.

The next step in our process consists in removing the reflecting coating from a selected area of the bulb to define a shell surfaced transmitting portion therein. The metallic coating may be removed in accordance with the process of our prior Pat. No. 2,247,432, granted July 1,

1941. In that process a solvent solution is applied to those portions of the bulb from which tional steps of manufacture.

the bulb neck with the it is desired to remove the metallic coating. We have suggested in Fig. 2 the step of removing metallic coating fromthe bowl end of a bulb intended for use in direct lighting. The coated bulb Ill is supported in upright position and the solvent solution is supplied through a vertical tube I5 surrounded by a larger tube or l casing I6 and containing concentrically a smaller withdrawing tube I1. A filter I8 surrounds the lower end of the tube I1 within the delivery tube I5 and acts to prevent splashing of the solvent solution as it is supplied to the bulb up to substantially the level of its maximum dlar'neter. If silver is employed as a coating for the bulb an acid solution, such as nitric acid, may be delivered through the tube I5. If aluminum is used as the metal of the coating a strongly alkaline solution may be similarly employed. As soon as the coating is dissolved the solution is withdrawn through the inner tube I1 and the bulb immediately washed out, with the result that a sharp line of demarkation is formed between the silver coating I8 and the bare shell surface transmitting portion 20 of the bulb.

Having completed the shell processing and metallic coating of the selected areas of the bulb in the manner above explained the bulb may now be employed inthe manufacture of an electric reflecting lamp by following the conven- The mount 2| and filament are sealed into filament substantially hooded by the reflecting coating I9. Preferably the filament will be of' the coiled coil type supplying a concentrated light source. The bulb is then exhausted, gas filled if desired, and sealed preparatory to being equipped with a metal base 22 of` any desired commercial construction.

It will be understood that the shallow rounded depressions making up the shell surface of the bulb are actually infinitessimal in size. The proccessed surface is of a somewhat lustrous light gray or pearl color in appearance and noticeably more transparent than a frosted surface. The surface as illustrated in Figs. 1 and 3 is drawn from microphotographs taken at a magnification of 500 diameters and then enlarged in the reproduction.

In addition to providing an electric reflecting lamp supplying a substantially uniform light pattern and one in which the transmitting portion of the lamp is not objectionably brilliant when the lamp is in use, we have substantially increased the illuminating efficiency of the lamp by reducing the amount of light absorbed and diverted in its transmitting portion as compared with lamps heretofore commercially available.

is a division of our etching and then stripping the inner surface of aY bulb to provide a shell surface thereon, that is to say, a surface which when observed at a magnification of 300 to 500 appears to comprise shallow, rounded, contiguous depressions orY hollows, varied in size, irregular in shape and bounded by slightly curved and straight lines extending in all directions and meeting at vertices sometimes in pairs and sometimes in greater numbers, ap- Dlylng a reflecting metallic coating over the processed area of the bulb surface, and then chemicalhr dissolving part of the coating to provide a translucent area in the bulb, entirely free from the reflecting coating.

2. A process of making reecting lamps, which includes the steps of frosting the inner surface of a bulb and subsequently stripping the bulb surface to produce a relatively smooth irregular nification of 300 to 500 appears to comprise shal- The intensity of illumination derived from a Y lamp constructed in accordance with our invention is about 16% greaterthan that derived from a commercially frosted lamp of identical size and rating.

While it is not practicable completely to remove a metallic coating from a shell surface by mechanical means, it is possible by using a scraping tool to form a translucent spiral or other markings in the coated area of a bulb processed as herein disclosed if it should be desired to s ecure the luminous appearance of the coated portion of the bulb as disclosed in the prior patent of Birdseye No. 2,074,888, March 23, 1937.

The process of our invention is herein illustrated as carried out upon a pear-shaped bulb, but it may, of course, be usefully applied to the manufacture of any lamphaving a'metallic re- 75' contour of shallow rounded depressions, applying a metallic reecting coating to the irregular surface thus produced, and then chemically dissolving and removing the metallic coating from a defined area of the processed bulb surface to form laglbuncoated light-transmitting portion -in the 3. The process of making reflecting electric lamps which includes the steps of chemically etching and stripping the inner surface of a bulb to provide a shell surface thereon, that is to say, a glass surface which when observed at a maglow, rounded, contiguous depressions or hollows. varied in size, irregular in shape and bounded by slightly curved and straight lines extending in all directions and ,meeting at vertices sometimes in pairs and sometimes in greater numbers,

and then applying to said surface a metallic reflecting medium thereby forming a diffusing reflecting surface in the lamp.

4. A process of making reflecting electric lamps which includes the steps of applying a metallic reflecting coating to the inner surface of the bulb thereby forming a reflecting surface therein, and prior to the application of said metalhc coating, forming a transmitting area for the reflected -rays by chemically etching and then stripping the inner surface of the bulb to present a glass surface which when observed at a magnication of 300 to 500 appears to comprise shallow, rounded, contiguous depressions or hollows, varied in size, irregular in shape and bounded by slightly curved and straight lines extending m all directions and meeting at vertices sometimes in pairs and sometimes in greater numbers, the said transmitting portion of the bulb being effective to transmit more than 25% of the light wmcnwoum be transmitted by a siml fiar transmitting area of clear glass.

CLARENCE BIRDSE Y E. PINCUB DEREN' lfleeting coating directing light rays through a Patent-No." 2,'.527,`978.

of the above unibered patent re CERTIFICATE 'QF CORRECTION. August 2h. 19115.

CLARENCE BIRDSEYE, -ET AL.

It is hereby certified v'that err-or appeers in the pritedsl's'eci'ficetion column, line 59, for "hubread jbulbg and 'second column., line 27, for ser- No., 101,915" read user. No. 191,u95; and 'that che said Letters Patent should be rea'd with this Correction therein that:- the same may oonfonn to the record of-the casein the Paten-t Office...v

Signed and sealed this 12th day ofOctober, A. D.- 1.9145.l

Henry Van Arsdele, f

(Seal) Acting Commissioner of Potente.

quiring correction as follows: Page 2, first 

